This invention relates to a process for producing an ammonium polythiomolybdate or a hydrate thereof of the formula (NH4)2Mo3S13.n H2O. More particularly, it relates to a process for producing ammonium polythiomolybdate which can be carried out economically on a commercial scale.
Ammonium polythiomolybdate has found use as a precursor in the preparation of molybdenum dithiocarbamate additives for lubricants.
U.S. Pat. No. 3,764,649 discloses the preparation of ammonium polythiomolybdate of the formula 3MoS4.2NH4OH by reacting an aqueous ammoniacal solution of ammonium molybdate and ammonium polysulfide at 175-220° C. and 300-700 psig. U.S. Pat. No. 4,604,278 teaches the production of ammonium tetrathiomolybdate by reacting an ammoniacal molybdate solution with hydrogen sulfide gas in a closed system.
Heretofore, the process commercially practiced for making ammonium polythiomolybdate has involved the use of ammonium sulfide which results in the formation of ammonium thiosulfate as an undesired impurity which must be removed.
Therefore, a simpler process for producing ammonium polythiomolybdate economically on a commercial scale and which avoids thiosulfate formation would be highly desirable and an advancement in the art.